Back to: Botany 200 Level
Hello, brilliant learner! Have you ever wondered why some plants bend toward sunlight, why fruits ripen, or how roots know to grow downward? The secret behind these amazing plant behaviours is plant hormones—special chemical messengers that control growth, development, and responses to the environment.
Today, we’ll learn about the major plant hormones, what they do, and how they help plants survive.
Overview of major plant hormones
What Are Plant Hormones?
Plant hormones (also called phytohormones) are natural chemicals that regulate growth, development, and responses in plants. Even though plants don’t have brains like humans, these hormones help them react to their surroundings!
There are five major types of plant hormones:
Auxins – Promote growth and bending toward light.
Gibberellins – Help plants grow tall and break seed dormancy.
Cytokinins – Stimulate cell division and delay ageing.
Abscisic Acid (ABA) – Helps plants survive stress.
Ethylene – Controls fruit ripening and leaf fall.
Functions of Major Plant Hormones
1. Auxins – The Growth Booster
Helps plants grow taller.
Controls phototropism (bending towards light).
Promotes root development.
Example:
If you place a potted plant near a window, you’ll notice it leans toward the light. This happens because auxins move to the shaded side of the stem, making those cells grow faster and bending the plant toward the light.
2. Gibberellins – The Growth Accelerator
Promotes stem elongation (especially in tall plants like sugarcane).
Helps seeds germinate by breaking dormancy.
Increases fruit size.
Example:
Ever wondered why seedless grapes are large? Farmers spray gibberellins to make them bigger!
3. Cytokinins – The Anti-Ageing Hormone
Stimulates cell division and growth.
Delays ageing in leaves.
Works with auxins to balance root and shoot growth.
Example:
In tissue culture (artificial plant growing), cytokinins help plants grow faster by encouraging cell division.
4. Abscisic Acid (ABA) – The Stress Manager
Helps plants survive drought by closing stomata.
Prevents seeds from sprouting too early.
Causes leaf fall in dry seasons.
Example:
During harmattan, many trees lose their leaves. This is because ABA levels rise, making leaves drop to reduce water loss.
5. Ethylene – The Ripening Hormone
Controls fruit ripening.
Helps plants shed leaves.
Increases when plants face stress.
Example:
Ever noticed how unripe bananas ripen faster when stored with ripe ones? That’s because ripe bananas release ethylene, which speeds up ripening!
Why Are Plant Hormones Important?
They regulate growth – Without auxins and gibberellins, plants wouldn’t grow properly.
They help plants adapt to the environment – ABA helps plants survive drought.
They control reproduction – Cytokinins and auxins ensure proper root and shoot development.
They improve agriculture – Farmers use ethylene and gibberellins to control fruit ripening and size.
Summary
Auxins control plant growth and bending toward light.
Gibberellins help plants grow tall and break seed dormancy.
Cytokinins promote cell division and delay ageing.
Abscisic Acid (ABA) helps plants survive stress and prevents early germination.
Ethylene controls fruit ripening and leaf fall.
Let’s Test Your Understanding:
- Which hormone makes stems grow longer and helps seeds germinate?
- How does auxin help plants respond to light?
- Why do trees lose their leaves during harmattan?
Great job, superstar! Now you understand how plants use hormones to grow, survive, and thrive. Keep learning, and see you in the next lesson!
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